1. Field of the Invention
The invention is directed to an improved fuel injection valve for internal combustion engines.
2. Description of the Prior Art
A fuel injection valve of the type with which this invention is concerned is known for instance from the German Patent Disclosure DE 27 11 391 and has a valve body, in which a hollow valve needle is disposed longitudinally displaceably in a bore. The hollow valve needle, on its end toward the combustion chamber, has a conical valve sealing or contact face, with which it cooperates with a conical valve seat that forms the end of the bore toward the combustion chamber. In the hollow valve needle, an inner or second valve needle is longitudinally displaceable and likewise has a conical valve contact face and cooperates with the valve seat. Both the hollow valve needle and the inner valve needle control the flow of fuel to at least one injection opening each, through which fuel is injected into the combustion chamber of the engine.
In the fuel injection valve known from DE 27 11 391, the tip of the hollow valve needle is flattened, forming an end face that is located in a radial plane of the hollow valve needle. However, this valve needle then has the disadvantage that a relatively large idle volume forms between the hollow valve needle, the inner valve needle, and the valve seat, and this has an unfavorable effect on hydrocarbon emissions of the fuel injection valve.
From DE 27 11 390, a fuel injection valve is also known in which the hollow valve needle has no flattened portion but instead comes to a point at the end. This does reduce the idle volume and thus has a favorable effect on hydrocarbon emissions from the engine but results in a disadvantage that the inner needle can easily become jammed in the outer needle. Because of the contact of the hollow valve needle with the conical valve seat, deformation of the hollow valve needle radially inward readily occurs, so that the already very small annular gap between the valve needle and the hollow valve needle is reduced still further. This can result in increased wear between these two components supported slidably displaceably relative to one another, and this shortens the service life of the fuel injection valve.